1. Field of the Invention
The present invention relates to the methods and processes for splitting pistachios which have not opened naturally to thereby make the pistachios desirable for commercial sale.
2. Description of the Prior Art
Pistachios are the seed of a dioecious tree of the cashew family. They include an edible kernel or meat which is surrounded by a hard smooth shell which is further covered by a soft hull. In spring, the female tree produces clusters of flowers that are pollinated by the male tree. A viable embryo, or seed, is formed in each pollinated flower. Consequently, a single cluster can have up to hundreds of viable embryos. Two distinct layers protect each embryo. There is an inner layer which becomes the hard shell, and the outer layer which later becomes the soft hull. The embryo itself becomes the edible meat or kernel of the nut.
The shells of pistachios split during late stage of seed development. Shell splitting ordinarily begins around July or early August, and continues into September. Pistachio shells have a visible line or suture that runs parallel to the longitudinal axis of the shell connecting the apex of the nut to its base. This seam demarks the line of dehiscence of the pistachio shell and is where the shell naturally opens to discharge the kernel. The base is the point at which the nut is attached to the cluster. During development, nutrients are transported through the base to the embryo. The base of the pistachio nut is visually distinct. It may be up to one eight of an inch (⅛″) in diameter. Its total surface area is a small fraction of the total surface area of the nut, yet it is far more porous than the rest of the shell. The natural splitting or shell detachment process in pistachios ordinarily starts at the apex of the nut and progresses along the suture toward the base.
Typically, upon arrival at a processing plant, hulls of pistachio nuts are immediately removed, and the remaining kernel and shell are dehydrated. As a result of dehydration, the kernels shrink thereby creating an air pocket within the shell. The shells of some pistachios naturally split when dehydrated, and are separated and removed from the closed-shell nuts. The closed-shell nuts then undergo further processing. The closed-shell pistachios are frequently non-symmetrical and ovoid to oblong in shape. They may be three-eighths of an inch (⅜″) to three-fourths of an inch (¾″) wide, and one half an inch (½″) to one inch (1″) long, depending on the variety.
Natural looking splits may be induced by applying external force either perpendicular to the axis of the suture in the vicinity of the apex, or parallel to the axis of the suture at either the apex or the base. An external force applied to a pistachio shell in any other direction may not split along the suture, may shatter the shell, or may induce no split at all. On the other hand, internal forces such as those generated during late stage seed development or during germination always split the shell along the suture producing natural looking splits.
The commercial salability of pistachio nuts depends in large part upon whether or not the shells are split, whether the splits look natural or induced, and the degree of splitting. A significant portion of a normal crop of pistachio nuts will remain closed even after processing. The value of closed-shell pistachio nuts is significantly less than that of the split nuts. As a result, there exists a need for efficient and reliable techniques to split unopened pistachio nuts in a uniform manner so that they resemble naturally opened nuts. However, it is important that pistachio opening processes and equipment be capable of quickly and efficiently splitting a large number of nuts, and that the process or equipment does not crack the shells of the unopened pistachio nuts other than along the sutures.
From early times through the present, pistachios have been hand split. Many hand devices are understood to be used such as pliers and the like to squeeze the nut until it splits. It has also been known in the art to soak the nuts in water. The shells of the pistachio are water permeable, and when hydrated, the shells become less brittle. After soaking, the shells are less likely to split improperly or shatter. Another traditional method involves soaking the closed shell pistachio nuts and then allowing the nuts to be dried by the sun. This method causes some of the shells to open along the suture.
A number of modern devices and processes have been devised for artificially splitting pistachios. The use of an apparatus to apply physical pressure to the shell of a pistachio to cause splitting is well known in the art. For instance, a known mechanism passes the nuts through a tapered area between a rotating conical mandrel and a concentrically arranged cylinder. The nuts must be distorted in compression to pass beyond the mandrel. This distortion is intended to split the nut artificially.
Another method has been devised which includes moisturizing the closed shell nuts to soften the shells, making them more resilient. These kinds of processes are described in U.S. Pat. Nos. 4,961,947 and 4,183,967. In the '947 patent, the pistachios with softened shells are released from a moisturizer and fed to a splitter. The nuts drop into individual cradles which are U-shaped in cross section and have an elongate axis extending between a movable splitting head and a stationary splitting jaw. The softened shells of the pistachio nuts are split by the mechanical pressure placed on the ends. Once split, the nuts are then dried and otherwise processed for sale. The description in the '967 patent differs slightly by applying pressure to the nuts with softened shells and splits the shells through the combination of the release of pressure and heat. Disadvantages remain with both of the aforementioned processes. By applying mechanical pressure, especially if the force is applied to the nut in the wrong position, the shell might not split along the suture, may shatter, or may not induce a split at all. Also, considerable time is spent soaking the shells of the nuts, typically at least an hour, thereby delaying the splitting process and requiring further drying before the nuts are ready for packing and shipment.
Another problem that arises in pistachio processing is that some nuts partially open, but not the extent needed to be commercially valuable. The shells of such nuts separate slightly along the longitudinal suture, but not to the extent necessary for the end user to remove the kernel or meat. Conventional ways to increase the split of the shell involve soaking the nut for an extended period of time and the allowing the nut to dry. This process is very time consuming as the pistachios must be soaked for a relatively long period time to allow the shells to become hydrated, and then dried for another relatively long period of time.
It is therefore desirable to provide a process that is capable of splitting pistachio shells in a quick, efficient manner that ensures a split along the longitudinal suture of the shell. It is also desirable to provide a process that is capable of further splitting partially open pistachio shells to make them commercially marketable.